1. Field of the Invention
This invention relates to nerve stimulation by electrically applying high frequency (radio frequency) energy to a localized region of a body. In particular, this invention relates to a flexible catheter or lead for treatment of a nervous system. More particularly this invention relates to a flexible epidural catheter and a method for applying pulsed radio frequency electrical energy to a region in the spinal canal. A fully implantable embodiment of the catheter further comprises a transducer being adapted to be subcutaneously implanted.
2. Description of Related Art
Catheters are known technical medical products which are manufactured for various intended purposes of usage in diagnostics or therapy. For instance, epidural catheters are known which can be inserted by a physician into the epidural space in the region of the spinal canal so as to be able to inject pain-killing drugs, for example. Such a method is particularly applied in treatment of chronic pain. The catheter can remain in the body for a time period of 1 to 30 days, for example, and the injection of the drugs can be effected through external or implanted pumps.
Instead of catheters also electrodes are used in therapy of chronic pain. Thus, electrodes for implantation are known, which are connected to a pulse generator for permanent stimulation of the spinal cord or the nerves. There are also known electrodes for stimulation which are connected to a transducer that is to be subcutaneously implanted. In this case the pulses of the generator are transmitted inductively to the transducer through the skin of the patient.
Moreover, special needles are known which are connected to a generator of pulsed high frequency. Such special needles and high frequency generators are used to trigger the release of pain-inhibiting substances in the spinal cord by selectively stimulating nerves, thereby effecting a pain treatment.
However, usage of these rigid special needles is frequently limited due to anatomical reasons or is avoided because of the risk of injury at introducing the special needles.
From European patent application EP 1 181 947 A2 an epidural catheter is known having at least three electrodes arranged in line. The electrodes serve to electrically stimulate nerves or the spinal cord. A channel for administration of drugs can be provided to allow for injecting pain-killing drugs in addition to the electrical stimulation of the spinal cord.
With the previously mentioned apparatuses operating with electrical stimulation by means of pulses or, in the case of the special needles, by means of pulsed high frequency, control of the effect of the stimulation is solely by feedback from the patient. The mode and intensity of the stimulation is determined on an empirical basis. However, an upper limit of the intensity of the stimulation is given by possible damage or destruction of the tissue and varies depending on the location and the design of the catheter or special needles and on the structure of the surrounding tissue. Hence, there is no definite correlation between the parameters of the applied pulses and the limit where damage occurs, so that a margin of safety has to be observed. The mentioned deficiencies also pertain to the documents acknowledged below.
U.S. Pat. No. 4,379,462 to Borkan et al. shows a catheter electrode assembly for spinal cord stimulation which, unlike the present invention, does not include a channel for drug delivery. Frequencies ranging from 10 to 1400 Hz are applied in the stimulation.
International application WO 92/07605 shows an epidural catheter intended to be implanted either temporarily or permanently. In a permanently implantable embodiment, the catheter includes an implantable pulse generator and, at a separate branch of the catheter, an implantable drug reservoir.
U.S. Pat. No. 5,423,877 to Mackey shows a catheter for use in acute pain management intended for electrical stimulation of the epidural space of the spinal cord. The catheter comprises a conduit for delivery of drugs. The catheter produces a longitudinally elongated electrical field, as leads of the catheter will electrically stimulate a longitudinal distance of from 10 to 15 cm. However, this is not suitable for selective stimulation of nerves.
U.S. Pat. No. 5,374,285 to Vaiani et al. discloses a spinal electrode catheter which can be connected to a stimulator.
U.S. Pat. No. 5,081,990 to Deletis shows a catheter for spinal epidural injection of drugs and measurement of evoked potentials. Measuring electrodes located on the tip of the catheter are connected to a voltage detector. The electrodes are, however, not adapted for electrical stimulation.
German patent application DE 36 02 219 A1 shows a flexible epidural neuroelectrode comprising a channel with lateral apertures. The electrode or catheter allows to administer pharmacological solutions epidurally and to measure the evoked spinal potentials at the same time (spinal cord monitoring). The electrode is, however, not adapted for electrical stimulation.
European patent application 1 145 731 A2 shows a multi-lumen, multi-functional catheter system. The catheter system is intended for use for a therapy of the parenchymal tissues of the brain. Amongst the generally mentioned uses is sampling of fluids within the extracellular and interstitial spaces of the brain, spinal cord, or other body tissues, concurrently with drug delivery or electrical recording/stimulating. Information gathered by a sensing element or measuring device is received by a host computer to evaluate a treatment procedure or patient conditions around the locality of treatment. A treatment procedure would be evaluated either by an operator or by artificial intelligence. Possible sensing systems include thermometric sensing systems. However, unlike the present invention, the application EP 1 145 731 A2 does not provide for a flexible epidural catheter having electrical contacts for stimulation.
Unlike the present invention, none of the documents described above does provide for the usage of high frequency (radio frequency) energy for electrical nerve stimulation. Also none of these documents describes a flexible catheter comprising a temperature sensor disposed in the distal region of the catheter. Actually, only the European application EP 1 145 731 A2 mentions thermometry at all.